1. Field of the Invention
The present invention relates to a sterilizing composition usable for sterilizing a food-packing material such as a polyethylene terephthalate packing material, and also relates to a sterilizing method using the same.
2. Discussion of Background
Examples of an industrial sterilizing method for a polyethylene terephthalate packing material, particularly a polyethylene terephthalate bottle (PET bottle), include a hot packing method and an aseptic packing method.
The hot packing method comprises a system of sterilizing a packed content at an ultra-high temperature (UHT) and then packing the content into a container at 85 to 87xc2x0 C., and examples of pollutant bacteria include bacteria spores derived from a production line or a container. On the other hand, the aseptic packing method comprises a system of sterilizing a packed content at UHT and then packing the sterilized content into a chemically sterilized container under an aseptic environment (NASA Standard Class 100), and examples of pollutant bacteria include chemically tolerable mold or bacteria spores.
It is known that examples of an agent for sterilizing a packing material in the aseptic packing method include peroxide type compounds such as hydrogen peroxide, ozone or peracetic acid, and chlorine type compounds such as chlorine or sodium hypochlorite. Among them, peracetic acid is widely used since it has an immediate effect and a strong sterilizing power even at a low concentration, and also it has a wide antibacterial spectrum and achieves an excellent effect for sterilizing bacteria spores, molds or yeasts.
Molds, bacteria spores and the like are not produced in a container such as an aluminum can, a steel can or a glass bottle, wherein a packed content can be maintained in an anaerobic state, but in case of an air-permeable PET bottle, the anaerobic state can not be maintained during storing for a long term, and there is a fear that anaerobic bacteria spores such as bacillus or molds such as chaetomium are produced. In order to prevent the production of these bacteria in a food-processing step, it is necessary to raise a temperature or a concentration of a sterilizing agent or to prolong a treating time.
However, if a concentration of a sterilizing agent is raised, there is a problem that a treating agent such as peracetic acid, hydrogen peroxide or acetic acid is likely attached or remained on a food-packing material even after sterilizing and washing steps. Also, if a temperature is raised, there are problems that a PET bottle or the like tends to be deformed by heat and consequently that a heat resistant packing material must be used.
In order to solve these problems, JP-A-10-323385 proposes a two step-sterilizing method comprising a combination of a sterilizing step of using a peroxide such as peracetic acid and a sterilizing step of using decyldimethyl ammonium chloride, but this method simply aims at achieving a synergistic effect of two kinds of sterilizing agents.
The present inventors have noted that the above problems can be solved and peracetic acid can be used substantially at a low concentration by improving a sterilizing power of a peracetic acid aqueous solution.
An object of the present invention is to discover a material which can improve a sterilizing power of a peracetic acid aqueous solution and to provide a sterilizing composition (for a food-packing material) which can stably sterilize with peracetic acid at a substantially low concentration without changing an apparatus, an equipment or sterilizing conditions, and also to provide a sterilizing method using the same.
The present inventors have intensively studied in order to achieve the above object, and discovered that a sterilizing power of a peracetic acid aqueous solution can be enhanced (achieving a synergistic effect) by adding a specific compound to an aqueous solution containing peracetic acid, hydrogen peroxide and acetic acid, and the present invention has been accomplished on the basis of this discovery.
The present invention provides a sterilizing composition for a food-packing material such as polyethylene terephthalate, characterized by containing the following components (1) and (2):
(1) an aqueous solution containing peracetic acid, hydrogen peroxide and acetic acid, and
(2) a peracetic acid sterilizing power-improving agent comprising one or two or more compounds selected from the group consisting of esters obtained from a C2-C8 aliphatic acid and a C2-C8 aliphatic alcohol, C2-C8 aliphatic alcohols and aliphatic alcohols having a benzene ring.
Further, the present invention provides a method for sterilizing a food-packing material, which comprises contacting a food-packing material with a sterilizing composition containing the following components (1) and (2) and then washing the food-packing material with a sterilized water:
(1) an aqueous solution containing peracetic acid, hydrogen peroxide and acetic acid, and
(2) a peracetic acid sterilizing power-improving agent comprising one or two or more compounds selected from the group consisting of esters obtained from a C2-C8 aliphatic acid and a C2-C8 aliphatic alcohol, C2-C8 aliphatic alcohols and aliphatic alcohols having a benzene ring.
Still further, the present invention provides a sterilizing composition characterized by containing the following components (1) and (2xe2x80x2):
(1) an aqueous solution containing peracetic acid, hydrogen peroxide and acetic acid, and
(2xe2x80x2) a peracetic acid sterilizing power-improving agent comprising one or two or more compounds selected from the group consisting of esters obtained from a C3-C8 aliphatic acid and a C3-C8 saturated aliphatic alcohol, C2-C4 aliphatic alcohols, C7-C8 aliphatic alcohols and aliphatic alcohols having a benzene ring represented by the following formula, 
wherein n is an integer of from 0 or 2 to 4, R1 is a hydrogen atom or a C1-C4 alkyl group, and R2 is a hydrogen atom, a C1-C4 alkyl group or a halogen atom.
Hereinafter, the present invention is described in more details.
A sterilizing composition of the present invention for a food-packing material can be prepared by adding a peracetic acid sterilizing power-improving agent to an aqueous solution containing peracetic acid, hydrogen peroxide and acetic acid previously prepared. That is, it is preferable to prepare the sterilizing composition of the present invention for a food-packing material by diluting the previously prepared aqueous solution containing peracetic acid, hydrogen peroxide and acetic acid so as to provide a predetermined peracetic acid concentration and then adding a predetermined amount of the peracetic acid sterilizing power-improving agent thereto. If the sterilizing composition is prepared in this manner, it provides a concentration which can be used as it is for a sterilizing step.
Among the peracetic acid sterilizing power-improving agents used in the present invention, examples of esters obtained from a C2-C8 aliphatic acid and a C2-C8 aliphatic alcohol include ethyl acetate, propyl acetate, amyl acetate, isoamyl acetate, ethyl propionate, butyl propionate, isoamyl propionate, ethyl butyrate, isoamyl butyrate, ethyl valerate, ethyl hexanoate, amyl hexanoate, isoamyl hexanoate, ethyl enanthoate, ethyl caprylate, amyl caprylate and isoamyl caprylate.
Examples of a C2-C8 aliphatic alcohol include ethanol, propanol, isopropyl alcohol, butanol, n-amyl alcohol, n-hexanol and n-heptanol.
Also, examples of an aliphatic alcohol having a benzene ring include preferably an alcohol represented by the formula, 
wherein n is an integer of from 0 to 5, R1 is a hydrogen atom or a C1-C4 alkyl group, and R2 is a hydrogen atom, a C1-C4 alkyl group or a halogen atom.
More particular examples include benzyl alcohol, methylbenzyl alcohol, ethylbenzyl alcohol, isopropylbenzyl alcohol, tert-butylbenzyl alcohol, chlorobenzyl alcohol, 2-phenyl ethanol, 3-phenyl-1-propyl alcohol, 2-phenyl-1-propyl alcohol, 1-phenyl-1-propyl alcohol, 4-phenyl-1-butanol and phenyl pentanol.
Among them, ethanol, propanol, benzyl alcohol and phenyl butanol are particularly preferable in respect of their performances of improving a sterilizing power of peracetic acid and their solubility.
Among these peracetic acid sterilizing power-improving agents, one or two or more compounds selected from the group consisting of esters obtained from a C3-C8 aliphatic acid and a C2-C8 saturated aliphatic alcohol, C2-C4 aliphatic alcohols, C7-C8 aliphatic alcohols and aliphatic alcohols having a benzene ring represented by the following formula, are suitably usable for sterilization of materials other than a food-packing material: 
wherein n is an integer of from 0 or 2 to 4, R1 is a hydrogen atom or a C1-C4 alkyl group, and R2 is a hydrogen atom, a C1-C4 alkyl group or a halogen atom.
Also, a sterilizing composition having a sterilizing power improved (for a food-packing material) can be obtained by incorporating an anionic surfactant into a sterilizing composition containing the above components (1) and (2) or (2xe2x80x2) (for a food-packing material), and therefore, an anionic surfactant may be optionally incorporated therein.
Examples of an anionic surfactant includes a sulfonate type anionic surfactant such as an alkylsulfonate, an alkylbenzenesulfonate, a dialkylsulfosuccinic acid ester salt or an xcex1-olefin sulfonate, a sulfate type anionic surfactant such as a higher alcohol sulfuric acid salt (an alkyl sulfate) or a polyoxyethylene alkyl ether sulfate, and a carboxylate type anionic surfactant such as a polyoxyethylene alkyl ether carboxylate. These surfactants sometimes generate foams, and if the generation of foams is not preferable, their use may be optionally controlled.
With regard to a concentration of each component of a sterilizing composition used for a sterilizing step (for a food-packing material), peracetic acid is used at a concentration of from 1,000 to 4,000 ppm, hydrogen peroxide is used at a concentration of from 1,500 to 30,000 ppm and acetic acid is used at a concentration of from 2,000 to 30,000 ppm, and a concentration of a peracetic acid sterilizing power-improving agent is varied depending on a kind of a peracetic acid sterilizing power-improving agent used due to a difference in its solubility and is determined in view of its solubility, but is preferably from 1,000 ppm to 10%.
With regard to the concentration of a peracetic acid sterilizing power-improving agent, an easily soluble material such as ethanol, propanol, isopropanol, benzyl alcohol or methylbenzyl alcohol is used preferably at a concentration of from 1 to 10%, more preferably from 2 to 8%, since a sterilizing power of the sterilizing composition is more highly enhanced if its addition amount is increased. Also, a material having a relatively low solubility or a hardly soluble material such as amyl acetate, isoamyl acetate, isoamyl caprylate, ethyl butyrate, pentyl acetate or heptanol, is used preferably at a concentration of from 1,500 ppm to 1%, more preferably from 2,000 to 9,000 ppm, and it may be used in a suspension state depending on a case required.
When using an anionic surfactant, its concentration is preferably from 10 to 5,000 ppm, more preferably from 100 to 2,000 ppm.
A sterilizing effect of the above sterilizing composition (for a food-packing material) is more enhanced as a temperature of the composition is raised, but a satisfactory performance for sterilizing mold, heat-resistant bacteria spores and the like deposited or generated on a food-packing material can be fully achieved at a temperature of from 40 to 65xc2x0 C.
The sterilizing composition of the present invention (for a food-packing material) is suitable for sterilizing a food-packing material, particularly a polyethylene terephthalate packing material such as a polyethylene terephthalate bottle, and the sterilization of a PET bottle is carried out for example as illustrated below.
(1) A sterilizing composition (chemical solution) of the present invention for a food-packing material is sprayed on the outer surface of a PET bottle to wash the outside of the bottle.
(2) Thereafter, the sterilizing composition (chemical solution) for a food-packing material at a temperature of from 40 to 65xc2x0 C. is sprayed or fully filled into the inside of the PET bottle to sterilize the inside of the bottle.
(3) After discharging the sterilizing composition (chemical solution) for a food-packing material, the PET bottle is washed with a sterilized water in order to remove the sterilizing composition (chemical solution) for a food-packing material attached to the inside and the outside of the PET bottle.